Juan Manuel Fangio in a Mercedes W196 in the vintage car race before the United States Grand Prix West held on March 28, 1976 in Long Beach, California. (Photo by Alvis Upitis/Getty Images)

Sir Stirling Moss chats with five time world champion Juan Manuel Fangio in his Mercedes W196 grand prix car during vintage race festivities at the inaugural United States Grand Prix West on March 26, 1976 in Long Beach, California. (Photo by Alvis Upitis/Getty Images)

Juan Manuel Fangio in a Mercedes W196 at the vintage car race before the United States Grand Prix West held on March 28, 1976 in Long Beach, California. (Photo by Alvis Upitis/Getty Images)

A Mercedes-Benz car that Juan Manuel Fangio drove to two Grand Prix victories sold today for 19.6 million pounds ($29.7 million), a record for a car at auction.

The 180 MPH Mercedes was being sold by the Emir of Qatar, who acquired it from the German industrialist Friedhelm Loh about eight years ago, according to dealers with knowledge of the car. A spokesman in the Emir's office said he would not comment on personal matters.

The silver Mercedes W196 didn't carry a formal valuation at Bonhams's 20th-anniversary "Festival of Speed" sale. The London-based auction house only said the price was likely to be higher than the record $16.4 million paid for a 1957 prototype Ferrari Testa Rossa at Gooding & Co. in California in August 2011.

"You're in a club of one with this car," Dave Kinney, publisher of the U.S.-based Hagerty Price Guide, said about the Mercedes before the auction. "You can't race it with your fellow Ferrari GTO owners. It is a very significant piece of Grand Prix history. While its future use-potential is slight, it exudes the history of perhaps the greatest era in racing."

The straight-eight, 2½-liter Mercedes is a variant of the streamlined aluminum-bodied "Stromlinienwagen" in which Fangio won the 1954 French Grand Prix.

Open Wheels

The Argentinian-born driver used this more maneuverable open-wheeled version to win that year's subsequent German and Swiss Grands Prix, securing the second of five Drivers' World Championship titles. Mercedes-Benz produced 15 examples of the W196 for the 1954 and 1955 Grand Prix seasons, several of which have been retained by the company.

Apart from the paint finish and some replacement hoses, the car remains in the same condition as it was in 1955, Bonhams said.

The buyer was an overseas bidder on the telephone, with six under bidders. The market for historic autos continues to grow, boosted by wealthy individuals' appetite for alternative investments.

The HAGI index of exceptional classic-car prices advanced 1.84 percent to reach a new high of 194.34 in June, said the London-based www.historicautogroup.com, using data from auction, dealer and private transactions.

HAGI said that though the collector base for single-seat racers is smaller than that for classic road cars, wealthy enthusiasts are prepared to pay high prices for examples in well-preserved condition with prestigious histories.

There are about 10 million pre-1972 classic cars in the world, with auctions representing less than 3 percent of annual sales, the Michigan-based specialist insurers Hagerty said.

GTO Private Sale

The record price for any car remains the $35 million given by U.S.-based collector Craig McCaw for an apple-green 1962 Ferrari GTO 250 racer that had been made for the U.K. driver Stirling Moss. The private transaction, first reported by Bloomberg, took place in June 2012.

The 250 GTO coupe, created in 1962 to compete at the Le Mans 24-Hour and other Grand Touring car races, is regarded by collectors as the most desirable of all classic Ferraris. Just 39 were made. At least three have been sold privately for more than $30 million, dealers said. None has been offered at auction for more than 20 years.